1. Field of the Invention
This invention relates to the field of biometrics as well as storage and retrieval of the dynamics of handwriting on limited space media and it specifically relates to the storage, retrieval and verification of signatures preserving the dynamic information on small memory devices such as the back of a transaction card (credit, debit or ID card).
2. Description of the Related Art
In 1995, Kodak scientists presented an aggressive image compression technique for coding the photo of a credit card holder in one of the three 57-byte magnetic strips available on the back of conventional credit cards. A more important or perhaps complementary piece of information which should be stored on one of these strips is the signature of the individual. Currently, the signature is written on the back of the credit card and is available to any forger to see at the moment of making purchases. In addition, this is only a static image of the individual's signature and lacks the dynamic information such as velocity, order and pressure at different portions of the signature. This dynamic information can substantially increase automatic signature verification results.
In their patent (U.S. Pat. No. 5,466,918), Ray, et al. provide a method for storing a human image (a biometric on the back of a transaction card which allows less than 57 bytes of storage). Here, I provide a method and apparatus for storing the full dynamic information of an on-line signature on the same medium. This data may be used to render the image of the signature or to act as a biometric template verifying the full dynamics of the signer's motion while signing and not just the image. The image is easy to forge by practicing, but the dynamics such as changes in velocity at different locations in the signature are much harder to forge even for professional forgers. In a dynamic template the order of the points in the image is preserved as well as the speed at different points in each stroke of the signature.
Low quality tablets have recently been installed at many department store cash registers to obtain electronic signature samples from customers. These samples are, however, still being treated as images and their dynamic information is not being used. For on-line verification, part of the problem is the storage of the signature templates which would have to be done at a central location accessible to stores through a network. This would be an expensive system which although is quite warranted, will not be easily attainable in practice since many stores do not have network connectivity. A self-contained signature verification system would be made possible if the credit card of the individual included his or her signature sample electronically. The electronic information may also be used to render the signature on a screen for the store manager to review and compare against the individual's signature at the time of purchase.
Van Leer in his patent number U.S. Pat. No. 4,005,878 uses a moving surface while the signature is being created to change the shape of the signature to make forgeries hard. It uses the image of the signature and forfeits the usage of any dynamic information.
Nair, et al. in their patent number U.S. Pat. No. 5,428,210 discuss a scenario which requires that the signature (although compressed) be sent to a server to authenticate the card-holder. This is due to the inability of the compression scheme discussed the invention to produce small enough templates. Also, they again do not use the dynamic information of the signature. Price, et al. in their patent number U.S. Pat. No. 5,448,044 use the image of a signature. They talk about comparing the facsimile of the captured signature to the image signature signed on the back of the credit card. This does not use dynamic information. The dynamic information is quite important in reducing the possibility of a forgery. It also defeats the purpose of capturing the electronic signal since the forger will be able to see the signature on the back of the card and to practice forging it. Since only the image is used by an operator to match the two signatures, forgeries may be easily accomplished.
Beatson et al. in their patent number U.S. Pat. No. 5,892,824 are forced to use an IC card to be able to store the image of a signature as stated in their invention's description (stated toward the beginning of column 19). In this description they state that the image of the signature is different from the biometric template and state earlier in the patent that the image takes up about 500 bytes requiring an IC card. My invention provides a biometric template which not only includes the full dynamic information such as the velocity at different points in the signature (much harder to forge than just shape), it also provides an image of the signature to be displayed on the monitor of the merchant which may also be used by the merchant to verify the signature of the customer. This eliminates the need for having a handwritten signature in ink on the back of the credit card and makes the job of a forger much harder.
In this patent, as a matter of comparison, I will present a loss-less compression scheme which will produce coded signatures of requiring over 1000 bytes for coding an average on-line signature. This is not nearly enough for our objective of an upper limit of 57 bytes, but it certainly has its own applications.